Fix the archive code so that it compiles in a stricter mode.

utils/archive/entry.dart

Index: utils/archive/entry.dart
diff --git a/utils/archive/entry.dart b/utils/archive/entry.dart
index 3e570bfc796ed486577d2e23dde72170fe4f9a92..72faa7dd05d5cfd597a2e3cca61cef26c999c40b 100644
--- a/utils/archive/entry.dart
+++ b/utils/archive/entry.dart
@@ -68,7 +68,6 @@ class ArchiveEntry {
 
   /** The path to this entry on disk, */
   String get sourcepath() => _properties[3];
-  set sourcepath(String value) => _set(SET_SOURCEPATH, 3, value);
 
   /** If this entry is a symlink, this is the destination. Otherwise, null. */
   String get symlink() => _properties[4];
@@ -126,7 +125,6 @@ class ArchiveEntry {
    * change, and vice versa.
    */
   String get fflags_text() => _properties[13];
-  set fflags_text(String value) => _set(SET_FFLAGS_TEXT, 13, value);
 
   /** The filetype bitmask for this entry. */
   int get filetype_mask() => _properties[14];